I've started seeing this on a few of my addons.  A google search reveals a flap failure?  I'm not extending them above a high speed.  (white arc generally for props).  But XP doesn't show any failures.

I extend flaps (at a safe speed) and the plane drastically rolls to the right or left.  So much that I can barely maintain straight and level flight without full aileron deflection.

It's happened on the vflyte twin comanche, the aerobask viper jet

 

Anyone seen this?

Are the flaps symmetrically extended (visually)? Even better, you could check the datarefs for flap extension (using datarefeditor). Additionally, what if you click on "show flight model"? Is there any asimmetry in the lift vectors? Finally, you could output a flight model cycle and attach it here, so maybe we can have a look at it.

 

The visual flaps can look fine but the code says one is missing.  If you have remove flight surfaces (or something like that) when damaged checked in options, it will cause this on some models.  Some models are more sensitive to airspeed and flaps than others.  The SMS Beaver is a bear for this.

If you look at the damage log you can see if you've lost one of the flaps, but I'm pretty sure this is what is happening to you.  Just uncheck that box.  No reason to have it checked if some planes are going to be realistic about shedding airfoils.

Make sure you do not have contradicting settings at play.  Know this is XP. When I had things like this happen in FSX it was usually due to having controls settings in both FSX and FSUIPC or in Spad.Next, or all of the above.  Are conflicts like that possible with XP?

So I don't know what happened.  Frank - I'm guessing that's possible but I checked that I had no dup controls.

I disabled that option to give damage for over G forces.  Then just now I went back in the sim, and re-enabled it.  Now nothing is broken, everything is flying as I would expect.

The display shows symmetry with flaps down.  Now I want to break it and try it again to see what it looks like.  I really hate accidentally fixing things.

EDIT:  Yes I figured out what happened...  I must have slipped and extended the flaps above vfe (or whatever the v speed is) at some point earlier in the day.  Because I purposefully increased to 140 kias and extended the flaps and you can see what happened to the starboard flap and the display shows it too.  Still I think I'm going to disable that "feature."  

symflaps by ryan b, on Flickr

flapsdmg by ryan b, on Flickr