How to Reproduce the Bug:

In View → Options → Audio:

• Enable "Snap markers by default" under the Options section.
• Enable "Cursor time" and "Video Position" under Display Visual Options.

This can be tested with a dummy video or real footage. The bug occurs in both cases.

Bug Example:

On this subtitle line:

Dialogue: 0,0:17:37.54,0:17:39.27,Default,,0,0,0,,adzd

1. Select the line.
2. Seek to time 0:17:39.268 (frame 25397).
3. Snap the end time of the subtitle to the cursor time.

Expected: The subtitle should no longer be displayed.
Actual: The subtitle is still displayed at the cursor time.

Working Example (No Bug):

Dialogue: 0,0:00:11.14,0:00:14.18,Default,,0,0,0,,aaaaaaaaaaaaa

1. Select the line.
2. Seek to time 0:00:14.181 (frame 340).
3. Snap the end time of the subtitle to the cursor time.

Result: The subtitle is not displayed, as expected.

Additional Notes:

After some investigation, it seems this bug occurs when the time of the selected frame relative to the start or end of the subtitle is negative.
If the relative time is greater than or equal to 0, the bug does not occur.