Why is it flashing when switching frames?

I have my project set up in a few frames, ranging in size from 320*256 to 800*600. Every frame has the following layers:

00: detectors, 2-bit collision masks and stuff
01. world graphic (houses, trees, ground)
02. characters
03. world graphics overhead stuff
04. interface etc.

Whenever the character's detector bumps into the teleport detector, the game switches from current frame to another frame. Nothing spectacular.

The problem is, whenever it happens, the frames clearly flash for a split second and the bottom layer (collisions, etc) can be clearly seen for a moment - this looks really bad. With a subapp it's even worse - all the "under the hood" game mechanisms can be clearly seen in all their RGB glory (of course I used some horrible colours for detectors).

Why does this happen and how do I avoid it? using too many layers? Can't be, the most layer-intense frame has 8 layers (and the frame is a 800*600)... There aren't that many heavy objects either, half of them are invisible most of the time anyway. Also the "start of frame' actions are pretty light. So, out of ideas - anybody else had a similar problem?

I remember that this was a problem if a certain application setting is checked, but I can't remember what it was! Try toggling "Machine-independent speed", possibly?

I think it's on the list of things to fix, but I can't say for sure.

Just tested it and looks like there is some connection... calling up a subapp is still horrible though - the flash before the sub-application appears (when it's created) looks almost like a special transition + everything freezes for a second before it shows up! It became even worse ever since I added Window Control and resized the aplication to 200%. And it's a super light subapp, with just a few "Start of frame" events so I have no idea what's causing it.

Still, I'd like to have the machine independent speed checked in case somebody with an old comp wants to try the game...

After a few days of Desperate Struggle, I`ll have to give up and just mask it somehow hoping nobody will notice.

Just for the record, here are my conclusions:

1. In frame properties, looks like the "handle collision outside of the window" is swapped (meaning ticked = no, while logically it should be ticked = yes).

2. No matter what the resolution / full screen conditions, the Window Shape always uses the original size of objects... unless when it arbitrarily does not. The only solution I found was to make a few Actives used for masking that cover all the resolutions I can predict and restrict customer`s options for selecting resolutions. Bad.

3. This one I have no idea what to do with. When my subapp appears on screen and grabs the mask from the active, for a split second it very visibly flashes and looks like a bug. I tried all the "create before fade in", rearranging / hiding layers and objects etc and the only interesting but useless thing I found is that it flashes even more horribly if I put the layer that contains the mask and the Window Shape object on top (which is logical, I guess lower layers get drawn first).

4. Window Shape has tons of strange side effects. For example, if an object with a semi transparency is used as a mask for a frame, the semi-transparency suddenly gets ignored (I`m not saying the window should become semi-transparent, just that one wouldn`t expect the Active to lose its semi transparency). Or for example if one turns the visibility of the layer where the masking Active is - the Window Shape stops working. I guess there`s a technological reason for it but it certainly surprised me when I discovered it.

ok found out what's causing it and how to tame it:

Tick "No thick frame" and untick "Resize display to fill window size" and it doesn't flash anymore. Crazy.

I honestly see no reason why it causes the nasty flashing but here it is.