Fix DataTable.header_height reactive visual glitch and crash (#6128)

Author: darrenburns

CHANGELOG.md

@@ -23,6 +23,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 ### Fixed
 
 - Fixed issue where Segments with a style of `None` aren't rendered https://github.com/Textualize/textual/pull/6109
+- Fixed visual glitches and crash when changing `DataTable.header_height` https://github.com/Textualize/textual/pull/6128
 
 ## [6.1.0] - 2025-08-01
 

src/textual/widgets/_data_table.py

@@ -1160,6 +1160,9 @@ def watch_fixed_columns(self) -> None:
     def watch_zebra_stripes(self) -> None:
         self._clear_caches()
 
+    def watch_header_height(self) -> None:
+        self._clear_caches()
+
     def validate_cell_padding(self, cell_padding: int) -> int:
         return max(cell_padding, 0)