Regression in v5.1.0: Split/rebalance long lines creates new subtitle entries, while v5.0.0 does not

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Assessment

Difficulty
3/5
Estimated time
1-2 days
Newbie friendliness
58/100
Issue type
Bug
Clarity
Mostly clear
Activity status
Quiet
Tech stack
csharp
Domain
desktop

Research direction

Start in Tools -> Split/rebalance long lines and reproduce the issue with the same SRT file and settings from the report. Compare the subtitle entry count and individual timecodes before and after; done means only line breaks change, with no new entries or timing changes.

Written by the indexing model from the issue text.

Description

Version:
Subtitle Edit v5.1.0 (29 Jul 2026)

Problem:
When I use Tools -> Split/rebalance long lines, some subtitles are split into new subtitle entries.

Expected behavior:
Only line breaks should be rebalanced inside the same subtitle.
The number of subtitle entries and timing should remain unchanged.

Actual behavior:
The number of subtitle entries increases.
Example:
Before:
1000
00:39:41,790 --> 00:39:45,210
Finalmente posso viver a minha própria vida de verdade

After:
1034
00:39:41,790 --> 00:39:43,830
Finalmente posso
viver a minha própria

1035
00:39:44,190 --> 00:39:45,210
vida de verdade

The dialog reports:
Lines split: 0
Lines rebalanced: 65

Settings:

  • Split long lines: ON
  • Rebalance long lines: ON
  • Max number of lines: 2
  • Single line max length: 38
  • Unbreak subtitles shorter than: 35

Version 5.0.0 → Works correctly.
Version 5.1.0 → Splits subtitle into multiple subtitle entries and changes individual timecodes.
Same SRT file.
Same settings.
Expected behavior: only rebalance line breaks within the same subtitle.

Dominant language
C#
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