Sorry for no code sample, I can try to get a small sample at some point. But hoping someone has seen this behavior before.
I have a DHTMLxGrid (3.0) that was created from an HTML table. The column widths are set using grid.setColumnWidthsP. When you click on the header to sort the columns, it continually expands the widths of most of the columns. If I remove the setColumnWidthsP and allow the grid to calculate the widths, it works fine. Another issue that might be tied to it, the sort image never appears. Again both items work fine if the column widths are not set by percentages.
Please, check width of your HTML table. if it has the relative sizes it may expand to the parent. If the problem still occurs for you please, provide any kind of snippet or a complete demo, where the problem can be reconstructed. You can also try to create a snippet here: https://snippet.dhtmlx.com/5/