Based on re-doing some of my previous measurements in the thread
http://www.hitechcreations.com/forums/showthread.php?s=&threadid=176856, the P-51 flaps have been partially fixed, but still show a bug in version 2.08-1.
According to my new measurements, the discontinuity has been removed from the 4/5 flap position, and now kicks in at the full (5/5) flaps position. I also spot checked my control aircraft (Bf-109f4), and it has no such discontinuity at full flaps. I have not yet checked the F4U, but I bet it has no discontinuity either, as it didn't before, and no mention of changes to the F4U were in HTC's release notes.
FLAPS - v(mph) - t (s) - r(yds) - rate(dps) - comment
*******************************************
P-51b
0/5 159 150 371 12.0
1/5 156 152 369 11.8
2/5 150 151 352 11.9
3/5 139 156 337 11.6
4/5 128 157 313 11.5
5/5 120 204 381 08.8 jump in radius, r !!!
********************************************
Bf-109f4
0/4 139 143 309 12.6
1/4 140 142 309 12.6
2/4 133 139 288 12.9
3/4 124 139 268 13.0
4/4 108 139 234 12.9
********************************************
Again, this appears to be a bug because I am not aware that the P-51 was uniquely unmaneuverable at full flaps, when compared with say the Bf-109 or the F4U series, and I assume that this behavior is not intentional on HTC's part.
Hopefully, therefore they can further tweak the P-51 flaps, so the turn radius decreases further at full flaps, as in the other planes.