patch 8.0.0110
Problem:    Drop command doesn't use existing window.
Solution:   Check the window width properly. (Hirohito Higashi)
diff --git a/src/buffer.c b/src/buffer.c
index e5d2dde..e77fc04 100644
--- a/src/buffer.c
+++ b/src/buffer.c
@@ -4858,8 +4858,8 @@
 	    wpnext = wp->w_next;
 	    buf = wp->w_buffer;
 	    if (buf->b_ffname == NULL
-		    || (!keep_tabs && buf->b_nwindows > 1)
-		    || wp->w_width != Columns)
+		    || (!keep_tabs && (buf->b_nwindows > 1
+			    || wp->w_width != Columns)))
 		i = opened_len;
 	    else
 	    {