build 261 - an old bug returns

Well, the good news is that I've run 5 hours with this build, and haven't gotten a crash; that's pretty good!!

Unfortunately, I'm getting the old "injecting garbage at random locations" bug, which had seemed to be fixed in the past. At line 1969 of a 2248 line file .c file, I got 269 characters of garbage... following is a hex-dump of the four lines that were involved.

Notes:
1. the affected line originally contained only a { character
2. I have not edited anywhere near this line in weeks; this garbage was inserted at a random location in the file!!

00000: 20 20 20 20 75 69 6E 74 38 20 69 20 3D 20 30 55 | uint8 i = 0U |
00010: 3B 0A 20 20 20 20 66 6F 72 28 20 69 3D 31 3B 20 | ;. for( i=1; |
00020: 69 3C 6D 5F 68 65 61 64 65 72 4C 65 6E 67 74 68 | i<m_headerLength |
00030: 3B 20 69 2B 2B 20 29 0A 20 20 3F 3F 7B 00 69 6E | ; i++ ). ??{.in |
00040: 3F 3F 3F 02 01 00 05 00 20 20 20 20 7D 00 00 00 | ???..... }... |
00050: 3F 3F 3F 02 01 00 05 00 20 20 20 20 7B 00 00 00 | ???..... {... |
00060: 81 3F 3F 6D 00 00 67 00 21 01 00 00 6D 00 00 00 | ???m..g.!...m... |
00070: 3F 3F 3F 02 01 00 05 00 20 20 20 20 7B 00 20 2A | ???..... {. * |
00080: 3F 3F 3F 02 01 00 05 00 20 20 20 20 7D 00 6F 64 | ???..... }.od |
00090: 3F 3F 01 00 04 00 3F 3F 00 00 00 00 00 00 00 00 | ??....??........ |
000A0: 3F 3F 3F 42 01 00 01 00 3F 00 00 00 00 00 00 00 | ???B....?....... |
000B0: 3F 3F 3F 6D 00 00 3F 00 59 04 00 00 3F 00 00 00 | ???m..?.Y...?... |
000C0: 3F 3F 3F 6D 00 00 3F 00 2E 04 00 00 3F 00 00 00 | ???m..?.....?... |
000D0: 3F 3F 3F 6D 00 00 3F 00 4E 04 00 00 3F 00 00 00 | ???m..?.N...?... |
000E0: 3F 3F 3F 6D 00 00 3F 00 4D 04 00 00 3F 00 00 00 | ???m..?.M...?... |
000F0: 3F 3F 3F 6D 00 00 3F 00 55 05 00 00 3F 00 00 00 | ???m..?.U...?... |
00100: 3F 3F 3F 6D 00 00 3F 00 49 05 00 00 3F 00 00 00 | ???m..?.I...?... |
00110: 3F 3F 3F 6D 00 00 3F 00 58 04 00 00 3F 00 00 00 | ???m..?.X...?... |
00120: 3F 3F 3F 6D 00 00 3F 00 56 04 00 00 3F 00 00 00 | ???m..?.V...?... |
00130: 3F 3F 3F 6D 00 00 3F 0A 20 20 20 20 20 20 20 20 | ???m..?. |
00140: 2F 2F 63 73 75 6D 0A 20 20 20 20 20 20 20 20 73 | //csum. s |
00150: 75 6D 20 2B 3D 20 2A 28 73 74 61 72 74 2B 69 29 | um += *(start+i) |
00160: 3B 0A 20 20 20 20 7D 0A | ;. }. |

I also have garbage in files (not hex) from time to time at random locations. Srange characters.

I'm experiencing something similar with build 4.6.2 (2750).
I'm not sure when occurs but on a large file (~2MB, encoding UTF-16LE) I had sometimes the insertion of the character 0xFF00 at a random position, sometimes followed by garbage or a sudden truncation.
I know that this kind of bugs (typically caused by unchecked access to memory buffers) may be quite difficult to spot, unfortunately I don't have any more information to give.
Sadly this is an issue that endangers my work, so I am now searching for alternatives.